1. Field of the Invention
This invention relates to a control apparatus for a dental gas burner, and more particularly to a control apparatus which is adapted to determine combustion time of a dental gas burner as desired depending upon the number of contacts or touches with respect to the apparatus by an operator.
2. Description of the Prior Art
A dental gas burner is generally used for heating a dental article such as a dental equipment, dental chemicals, a dental material or the like. The dental gas burner causes the pollution of air in a consultation room and the waste of fuel gas when it is left ignited. Whereas, when the dental gas burner is unexpectedly extinguished, fuel gas is discharged to cause danger. Thus, it is desired that the dental gas burner is ignited every use and extinguished immediately after the use. However, such operation of the burner puts an operator such as a dentist to much trouble, thus, the burner is typically kept at a combustion or ignition state irrespective of the above-mentioned disadvantages.
In order to eliminate the foregoing disadvantage, a control unit using a photoelectric detector arranged in proximity to a gas injection nozzle of a dental gas burner has been proposed in Japanese Utility Model Application Laid-Open Publication No. 51092/1983 wich is adapted to allow the burner to automatically start combustion when the detector detects the approach of an article to be heated such as a dental equipment to the nozzle and permit the burner to be automatically extinguished when the article is away from the nozzle. The photoelectric detector comprises a light emitting element and a light receiving element. However, the conventional control unit is constructed in a manner such that the burner may carry out combustion only for a period of time during which an article is interposed between the light emitting element and the light receiving element to interrupt an optical path therebetween. Thus, the control unit has a disadvantage of readily causing malfunction because it causes the burner to be ignited when an unexpected article is interposed between the light emitting element and the light receiving element or it causes the burner to be extinguished when light other than that generated from the light emitting element is incident upon the light receiving element.
Also, another control unit has been proposed which utilizes a switch means. Such conventional control unit is constructed in such a manner that the burner is ignited to carry out combustion for a predetermined period of time when an operator touches the switch means directly or indirectly through a conductive article and then the switch means automatically closes a gas valve to extinguish the burner. The control unit is superior in decreasing malfunction to the aforesaid control unit. However, it has a disadvantage that it causes the workability to be significantly reduced or increases waste combustion of the burner because heating time required is not coincident with combustion time of the burner due to its constant combustion time.